Thoracic load carriage-induced respiratory muscle fatigue

We investigated the effect of carrying a 25 kg backpack upon exercise-induced respiratory muscle fatigue, pulmonary function and physiological and perceptual responses to exercise.

Nineteen healthy males performed 60 min walking at 6.5 km h⁻¹ and 0 % gradient with a 25 kg backpack (load carriage; LC). Following 15 min recovery participants then completed a 2.4 km time trial with the load (LC_TT) and on a different day, repeated the trials without the load [control trial (CON) and control time trial (CON_TT), respectively]. Respiratory muscle fatigue was determined by the transient change in maximal inspiratory (P _Imax) and expiratory (P _Emax) pressure prior to and immediately following exercise.

P _Imax and P _Emax were reduced from baseline by 11 and 13 % (P < 0.05), respectively, post-LC but remained unchanged post-CON. Following the time trial P _Imax and P _Emax were reduced 16 and 19 %, respectively, post-LC_TT (P < 0.05) and by 6 and 10 %, respectively (P < 0.05), post-CON_TT compared to baseline. Both forced vital capacity and forced expiratory volume in 1 s were reduced by 4 ± 13 and 1 ± 9 %, respectively, during LC when compared to CON. Relative to CON all physiological and perceptual responses were greater in LC, both post-LC and -LC_TT (P < 0.01). Time trial performance was faster during CON_TT (11.08 ± 1.62 min) relative to LC_TT (15.93 ± 1.91 min; P < 0.05).

This study provides novel evidence that constant speed walking and time trial exercise with 25 kg thoracic load carriage induces significant inspiratory and expiratory muscle fatigue and may have important performance implications in some recreational and occupational settings.